I am running into a strange problem when solving the 2D compressible Euler equations on a inclined wedge. To elaborate, my top boundary condition seems to emitting some type of instability. I have tried using Neumann BCs for the u,v velocities, but the issue still persists.

I am using a 2nd-order finite volume method on a curvilinear mesh (structured grid). My flux scheme is the Roe scheme with the Harten entropy fix. I have attached a movie that illustrates the problem.

I was curious if someone has any thoughts.

enter image description here


  • $\begingroup$ That looks like a shock instability which some schemes can suffer from. Can you try HLL flux which does not suffer from such problems, or even Rusanov flux. $\endgroup$
    – cfdlab
    Commented May 8, 2019 at 7:55
  • $\begingroup$ I don't want to be too nosy, ..but what kind of application is this for? A Mach 10 shock in a confined space?:-) $\endgroup$
    – MPIchael
    Commented May 8, 2019 at 12:44
  • $\begingroup$ I was able to implement the Rusanov flux. What I have found is that I need approximately double the number grids in the X direction than the Y for the instability to not occur. What I find strange is I have fully validated my code on an oblique shock over a ramp along with flow over a forward facing ramp. $\endgroup$
    – Simon
    Commented May 14, 2019 at 13:52


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